- Engaging an aircraft when it is landing, taking off, or on the ground is refereed to as vulching, and is not ok. Attacking a ground based vehicle, such as a tank, or ship, or someone who is in an aircraft but chooses to fire from the ground, does not count as vulching.
- Three flares is the common international signal to disengage. If, however, someone continues to attack you, or an unengaged aircraft, after deploying 3 flares, the signal may be ignored.
- Attacking unarmed civilian aircraft is seen as poor behavior. When a pilot is in a marked civilian aircraft, such as a 737, and is flying a normal route, the issue is unambiguous. Don't attack them. When someone flies an unarmed military aircraft, it is not considered polite to kill them, but they are not entirely civilian, and so this is something of a grey area. As a general rule, don't do it unless you are both engaged in some kind of combat exercise, such as "escort the C-130". Attacking a civilian aircraft which has declared itself to be hostile is ok.
- Missile combat can be fun, but do show some restraint.
- Look out for furballs - large, multi-plane engagements in which anything, or near anything is permitted. There are generally some loose guidelines - propeller or jet aircraft, missiles allowed or disallowed, vulching permitted or not (assume not unless you are told otherwise.) These are great fun. Some involve teams, some do not. Just be sure to ask before joining in - people can become miffed when a private dogfight becomes a furball unexpectedly.
- Check the server's rules on engaging ground targets. If you can find targets that shoot back, go for those first. Avoid useful infrastructure objects, such as the VOR, if non-combat pilots are using them.
This covers most of the basics in the English community. Subsequent posts will expand on this knowledge base, and may add standards in other communities as well.